With the greatly increased concern about the quality of life brought by remarkable advances in science and technology, the significance of disease diagnosis and prophylaxis, quality assurance of foods and full monitoring of environment is ever increasing. As a result, there is a great need for quantitative measurement of organic or inorganic analytes of interests on site, and in fact, the ability to accurately determine levels of organic or inorganic analytes is indispensable for the diagnosis of diseases, specific quality control processes in the food chemistry or industrial chemistry fields, and the monitoring of pollutants in the environment industry. Many attempts have been made to improve accuracy in the quantitative analysis of organic, inorganic and biological material of interests.
Also, interest in techniques for handling and delivering very small amounts of samples or reagents has been increasing, as the micro scale analysis becomes possible due to the development of science and technology. Biosensor technology is receiving a great attention as a means for handling infinitesimal amounts of samples or reagents in a variety of research and development fields, for example, clinical tests, test for the freshness and contamination of foods, control in biological processes, environmental monitoring, etc., because it allows rapid and convenient analyses of various materials of interests.
A biosensor is a device for the detection of an analyte that combines a biological component, such as enzyme, microbe, antibody, natural or artificial receptor, DNA probe, etc., with a detector component, which is structured to associate a bio-substance with an electronic or physiochemical transducer, to react it with signal generating element to cause a physical change in electro active analyte, and to detect the analyte or the change in electrochemical, optical, thermal or piezoelectric way. Immunosensor, which is designed based on the principle of specific recognition of an antibody for an antigen, shows high selectivity and a low detection limit, and is thus attracting great attention as a diagnostic sensor for use in the medical field.
Immunosensors are primarily based on solid-phase sandwich enzyme immunoassay. In a solid-phase sandwich enzyme immunoassay, an antigen is bound to an immobilized antibody and is then associated at a different epitope with a secondary antibody-enzyme conjugate. The solid-phase sandwich enzyme immunoassay is known to have higher sensitivity than other immunoassays. For example, an immune response in a matrix which is used as a reaction site for a solid-phase competitive immunoassay may be interrupted due to the steric hindrance of other substances. In case of the sandwich enzyme immunoassay, however, an immune response occurs only at an epitope site, so that it is interrupted to a much lesser extent than in the competitive immunoassay, thus generating sensitive signal. In a sandwich enzyme immunoassay, pathogens, viruses, cells, etc., which retain analytes of interest, typically large-size proteins, are bound to immobilized antibodies, washed, and associated with a secondary antibody-enzyme conjugate. Therefore, the amount of the labeling enzyme remaining on the solid phase is proportional to the amount of the analyte. After the removal of the secondary antibody-enzyme conjugate by washing, the amount of the labeling enzyme can be detected by measuring the rate of reaction with a substrate. Showing better specificity and sensitivity, particularly for protein analytes, a sandwich enzyme immunoassay is widely applied to the analysis of clinically important blood proteins.
A lab-on-a-chip is a chemical microprocessor made by integrating many kinds of devices on a plate (or chip) that is only a few square centimeters in size and is made of glass, silicon or plastic using photolithography or micromachining, generally used in semiconductor technology. As such, the lab-on-a-chip can be used to conduct automated experiments at a high throughput, high efficiency and low cost.
This micro analysis system is emerging as an important technology in the pharmaceutical industry, which has recently grown sharply, because it can significantly reduce the cost and time necessary to search for new drugs. In addition, lab-on-a-chip is a core technology which can find applications in a variety of fields, including medical diagnosis instruments, bedside health monitoring devices, chemical or biological process monitoring, portable analytical equipment for testing for environmental pollutants, unmanned chemical/biological agent detection/discerning apparatuses, etc.
Conventional lab-on-a-chip sensors, however, have problematic structures in terms of mass production. In consideration of the fact that lab-on-a-chip technology is applied, in the most part, to disposable biochemical sensors, conventional structures are difficult to produce at low cost and high reliability. Further, conventional biosensors in lab-on-a-chip are complicated in structure because they use micro-valves, high voltage capillary electrophoresis, and/or combination of complicate miniaturized mechanical components for the delivery of fluid through channels and require washing processes.
Leading to the present invention, the inventors intensively researched the biosensors which are easy to produce, convenient to carry and simple in constitution and suitable for mass production, devised a convenient and practical lab-on-a-chip system that drives a sample by capillary phenomena sequentially through dividing channels and reservoirs containing antibody-enzyme conjugate and signal generating substrates, respectively, and through antibody immobilized electrodes to washing channels for total enzyme-linked electrochemical immunoassay once the sample is injected.